Section A. GENERAL
84. Heating with the Hot Oil Heater
There are many conditions which arise outside the heat exchanger which can cause poor heat transfer
through an external user to the hot oil heater.
When hot oil heater is set up for operation and a new 3 phase electrical power source is connected,
always check for rotation of blower and circulating pump motors. If rotation is not correct, change
any two electrical power leads to correct rotation.
Air trapped in piping and tanks will sometimes move into the oil stream causing the following conditions.
The pump will become noisy. The sound will give you the impression that there are foreign objects in the
pump. This condition is called cavitation. The pressure gauges will fluctuate wildly and the flexible lines
on the return to the strainer will move about. The pressure gauge at the heater discharge will register
other than normal operating pressure of about 35 psi because the pump is actually trying to compress this
air trapped in the lines. Small amounts will work out through the vent in the cold seal tank. The chief
cause of air entering the system is usually because the system is improperly filled. Therefore, make
certain the fluid level in the expansion tank is equal or above the line stenciled on the tank end, behind the
sight glass. If the air continues to enter the system during operation, check all pipe joints to the pump
suction to see that they are tight and not leaking.
Water will enter the system due to condensation after a unit has been shutdown for a prolonged period of
time or due to water in any makeup oil put in the system. When water is present in the system the hot oil
will create a popping or sizzling sound in the expansion tank. If the presence of water is detected, it is
wise to lower the temperature to 2500F until the water is boiled out and vented as a vapor. It is also
suggested upon starting after a prolonged shutdown, the unit be operated for an hour or so at a
temperature of 250°F before going on up to the operating temperature.
Valving. There are five operating valves located on the hot oil heater. They are identified as follows:
supply valve A - located on the heater front, pump valve C - located above the pump, on the pump
suction, makeup valve D - located in a 1 1/2 line from the expansion tank, entering the surge tank above
the pump, fill valve B - mounted between the pump valve and pump, with one end threaded for filling
system from an external source. In normal operation the pump valve is full open and the supply valve is
full open. Open the makeup valve from expansion tank to surge tank. Close fill valve.